1. Field of the Invention
The present invention relates to systems and methods for power line communication and in particular, systems and methods for wideband power line communication.
2. Related Art
With the growing use of digital content (e.g. MP3 audio, MPEG4 video and digital photographs) there is a widely recognised need to improve digital communication systems. Power line communication (PLC) is a technology that encodes data in a signal and transmits the signal on existing electricity power lines in a band of frequencies that are not used for supplying electricity. Accordingly, PLC leverages the ubiquity of existing electricity networks to provide extensive network coverage. Furthermore, since PLC enables data to be accessed from conventional power-outlets, no new wiring needs to be installed in a building (or different parts of a building). Accordingly, PLC offers the additional advantage of reduced installation costs.
Referring to FIG. 1, a household 10 typically has a distributed mains wiring system (not shown) consisting of one or more ring mains, several stubs and some distribution back to a junction box 12. For the sake of example, let the household 10 comprise four rooms 14, 16, 18 and 20. Every room 14-20 may have a different number of outlets and other mains connections. For example, room 14 may have only one connection 22, room 16 may have two connections 24, 26, room 18 may have three connections 28, 30, 32 and room 20 may have six connections 34, 36, 38, 40, 42, 44.
Accordingly, there are a variety of distances and paths between different power outlets in the household 10. In particular, the outlets most closely located to each other are those on multi-plug strips, and the outlets furthest away from each other are those on the ends of stubs of different ring mains (e.g. power outlets in the garden shed and the attic). Communication between these furthest outlets typically pass through the junction box 12. Nonetheless, the majority of outlets associated with a particular application (e.g. Home Cinema) are normally located relatively close together.
Because the channel capacity of a power line and connectors attenuates according to, amongst other features, the frequency of a transmitted signal, current generation PLC systems have been developed to transmit signals at relatively low frequencies (i.e. below 30 MHz) and thereby obtain suitable transmission distances. However, the use of such low transmission frequencies limits the maximum data throughput obtainable by PLC systems.
The processes of receiving analog signals and injecting modulated signals are treated differently by different PLC standards. Current approaches perform some analog conditioning to the signal-path (e.g. low-pass filtering for anti-aliasing or smoothing, or AC coupling to remove the low-frequency [<<1 KHz] high voltage content of the electricity mains). However, there are no analog systems available for combining two or more broadband PLC technologies that can work simultaneously.
A number of power line communication standards have been defined. These include the Homeplug 1.0/1.1 standards, the Homeplug AV standard, the CEPCA standard, the Digital Home Standard, IEEE 1901, and ITU-T G.9960.
In common with most communication systems, one of the main problems with prior art PLC systems is obtaining high throughput and wide coverage at reasonable implementation cost, whilst maintaining compatibility with existing technologies. Although a few PLC systems that provide transmission rates of hundreds of megabits per second are currently on the market, these systems have high implementation costs as they employ high bps/Hz modulation schemes (i.e. approximately 10 bps/Hz) which require high accuracy data converters, extremely linear interface electronics and increase the cost of the digital implementation due to the computational complexity of the modulation.
There is, therefore, a need for improved PLC systems that overcome the above and other problems.